Ever since workers began using electronic gas detectors, they have used instruments with pumps. The question of exactly when and how pumps should be used remains, even today.
Many people believe that every gas monitor should have a pump. They feel that without a pump, the gas monitor is less accurate, slower to respond and simply doesn’t detect as much gas. While having a pump on a gas monitor will not make it more accurate, quicker to respond or able to cover more area around you, it will make performing certain tasks remarkably easier and safer.
Pumps allow employees to easily pull the air from an unknown and potentially toxic or combustible atmosphere to a gas monitor location so that they can view the monitor’s results in an area that they know to be safe. Pumps literally keep them out of harm’s way. Once they’ve assessed the air sample using a pumped gas monitor and confirmed it is clear of any toxic or combustible gases, they may enter the tested area and perform any work that needs to be done there.
Situations Made Safer by Pumps
Often, there will be a vessel that is not very tall, but may span a distance of 30 ft. or more. In this type of confined space entry, a pump with an extendible probe allows workers to slowly advance into the space with the probe ahead of them, ensuring that the atmosphere is safe prior to entering further.
Other times, the vessel may be tall and narrow, requiring an entry from above. In this instance, using a pump and sufficient tubing will allow employees to check from above that the entire vessel has been completely emptied of any hazardous gases prior to entry.
With both of these examples, you are allowing the pump and sampling equipment to pull the air to the monitor prior to entry, making the operations safer.
We’ve seen how having a pump on a gas monitor can make operations easier and safer. However, having a pump does not increase the range of detection or the effectiveness of the gas monitor.
The gas monitor’s sensors still only will detect the gas with which they come in direct contact. Having a pump on a gas monitor does not increase the amount of gas the sensors see. Rather, the pump allows you to test the atmosphere at a distance from the monitor. Therefore, if you place two instruments next to each other and one has a pump with no tubing attached, it will not detect the hazardous gases any faster than the unit without the pump, and both units will read the same.
Downsides of Pumps
What is the downside of always using a pump? While the gas monitor will detect gas in the same manner whether it has a pump on it or not, a monitor with a pump certainly will be larger and heavier. Also, the pump will use some of the instrument’s battery, resulting in a shorter run time for the overall instrument. Since operators typically wear a gas monitor their entire workday, which could extend to 12 or more hours, having a gas monitor that is small, lightweight and runs the entire shift is critical. Most people would agree that it is better to save the pumped monitor for where it absolutely is needed.
Once you have decided that a pumped monitor is needed for tasks at your facility, you will want to make sure you have any accessories required to effectively use and protect your pumped monitor. If workers are doing a horizontal entry or using the pump to check areas that are difficult to reach, they should use a probe. This may be a lightweight polycarbonate probe, an extendable stainless steel probe or perhaps a probe designed to withstand high temperatures.
If they are doing a vertical entry, you will need some tubing. Commonly, you will see urethane and Teflon-lined tubing. Urethane tubing is suitable to sample gases with the exception of chlorine, chlorine dioxide, hydrogen chloride and volatile organic compounds (VOCs). Chlorine, chlorine dioxide, hydrogen chloride and VOCs can be absorbed by urethane tubing, leading to inaccurate readings. For this reason, Teflon-lined tubing is recommended for use with these gases.
Any time workers are using a pump with tubing, it is important to allow enough time for the gas sample to travel the length of tubing and diffuse into the sensors. A good rule of thumb is to allow two seconds for each foot of tubing, plus two minutes for the sensors to read and stabilize. That means if there is 30 ft. of tubing attached to the pump, it will be three minutes before you will get readings from the gas at the end of that tubing.
Another important tip when using a pumped gas monitor is to use a dust filter and water stop at the end of the tubing or probe. In addition to preventing damage from dust and debris, it will prevent liquid from being pulled into the pump motor should the end of the tubing get dropped into any liquids.
Whether you are working in a water treatment plant and verifying that a tank is free of gases prior to its maintenance, or checking for leaks among a number of hard-to-access valves and piping in a refinery, using a pumped gas monitor will keep you out of harm’s way. For personal monitoring applications where remote sampling is not required, consider sticking with a non-pumped monitor. EHS
Gregg Bako serves as an applications engineer at Industrial Scientific. He can be reached at [email protected]